21802409 has 2 divisors, whose sum is σ = 21802410. Its totient is φ = 21802408.

The previous prime is 21802397. The next prime is 21802411. The reversal of 21802409 is 90420812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16581184 + 5221225 = 4072^2 + 2285^2 .

It is a cyclic number.

It is not a de Polignac number, because 21802409 - 2¹² = 21798313 is a prime.

Together with 21802411, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21802439) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10901204 + 10901205.

It is an arithmetic number, because the mean of its divisors is an integer number (10901205).

Almost surely, 2^21802409 is an apocalyptic number.

It is an amenable number.

21802409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21802409 is an equidigital number, since it uses as much as digits as its factorization.

21802409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1152, while the sum is 26.

The square root of 21802409 is about 4669.3049804013. The cubic root of 21802409 is about 279.3625336472.

The spelling of 21802409 in words is "twenty-one million, eight hundred two thousand, four hundred nine".